This application is based upon and claims priority to German Patent Application 199 31 663.5 filed Jul. 8, 1999, which application is herein expressly incorporated by reference.
The invention relates to a process and device for treating small parts with a liquid treatment medium, especially for coating small parts or for chemically deburring the small parts, in a treatment machine. The machine comprises a closable container which includes a drum to receive the parts. The drum is rotatingly drivable and adjustable between an inclined axis position and a vertical axis position.
Processes and machines have been developed and produced by the Applicant for some time. Examples are found in the following patents: DE 31 21 397 C1, DE 32 30 108 C2, DE 34 20 859 C2 and DE 42 02 880 C1. In each of these cases, the perforated drum that receives the small parts is designed to be releasable from its driving means in the machine. Thus, the drum can be filled and emptied outside the machine. In consequence, the drum, together with the small parts, can be inserted into different machines with identical driving means. The machines serve to carry out different treatment stages. The different treatment stages are carried out in the different machines. The small parts are frequently oiled during mechanical production and then subjected to de-oiling and washing processes as well as to surface treatment processes. It is also possible for chemical deburring to take place between the processes.
With these treatment stages, small parts with cavities that are open on only one side often suffer from air inclusion in the cavities. As a result of inadequate cleaning and/or inadequate coating, this leads to defective regions on the parts. Eventually, this turns the small parts into rejects, for either purely visual reasons or because of a reduced functional ability. If these cavities are particularly small, even agitating the small parts in the drum driven in an inclined position cannot reliably eliminate the air inclusions.
It is an object of the present invention to provide an improved process and a machine to carry out the process which improves the quality of the treated small parts.
The inventive sequence of process stages includes: Filling the drum with small parts and evacuating the closed container; filling the container with a treatment medium, while the internal pressure is set to a value in excess of the steam pressure of the most volatile component of the treatment medium; inclining the axis position of the drum and rotatingly driving the drum at a low speed; and ventilating the container and setting the drum to the vertical position.
Depending on the process to be carried out, the treatment medium is a coating medium for surface coating or it is an etching fluid for chemical deburring.
By evacuating the container down to a very low internal pressure, for example, in the range of 20 millibar, even the cavities in the small parts are evacuated. Thus, any defect-causing air pockets cannot occur in the cavities when, subsequently, the treatment fluid is introduced into the container. The internal pressure is reduced to the lowest possible level feasible at technically acceptable efforts.
On the other hand, by setting the internal pressure to a higher vacuum level, for example, in the range of 40 millibar, the treatment fluid is prevented from boiling. This is due to the fact that 40 millibar is just in excess of the steam pressure of the most volatile component of the treatment fluid boiling at the lowest temperature. Thus, this prevents the occurrence of a new source of defects and ensures an effective treatment with a treatment fluid which is free from vapor bubbles. A higher vacuum level in the container, for treatment purposes, is partially set automatically by introducing the liquid volume. Renewed evacuation may possibly have to take place for pressure setting purposes.
The drum is rotatingly driven in the inclined axis position for a longer period of time. Next, the container is ventilated and the drum is moved into the vertical position. Accordingly, the defect-free coated parts can be lifted together with the drum from the machine. However, according to a preferred embodiment, first the treatment fluid is pumped off. The drum, in the vertical axis position, is then rotated at an increased speed in order to centrifuge the treatment fluid off the parts as far as possible. This prevents the treatment fluid from being carried over before the subsequent process stages are carried out in the same machine or in a different machine. The treatment process is preferably repeated several times before the drum with the small parts is finally removed from the machine. During the subsequent centrifuging operation, hot air can be blown into the container or the container can again be evacuated. This time it is evacuated down to an internal pressure which is lower than the steam pressure of the treatment fluid. This enables the small parts to dry as quickly as possible.
To complement the above process, it can be preceded by process stages of washing and rinsing the small parts in the same machine. The individual stages can fully correspond to the inventive process stages. A suitable washing or rinsing liquid is used in each case. In particular, in this case, too, it is proposed to evacuate the container prior to introducing the fluid to eliminate air inclusions. Also, the vacuum is set to a level which is in excess of the steam pressure in order to avoid the formation of vapor bubbles. In the same way that the treatment process is improved by the above measures, likewise the preceding washing and rinsing processes are also improved. Here, complete and defect-free moistening of the surfaces of the small parts including their cavities is ensured.
An inventive machine to carry out the above process has a container with a drum arranged in the container. The drum is adjustably rotatingly drivable between a vertical axis position and an inclined axis position. The drum is drivable at at least one lower speed in the inclined axis position and at at least one higher speed in the vertical axis position. An airtight closure of the container is also possible. A mechanism to evacuate the container is included. Further, the machine includes a mechanism to introduce a liquid treatment medium when the container is in a closed and evacuated condition. A mechanism to pump off the liquid treatment medium from the container and a mechanism to control the internal pressure in the container are part of the machine.
The container is connected by pipelines to one or several tanks of the proposed treatment fluids. The tanks contain pumps and shut-offs. Furthermore, the container is connected, via suitable pipelines, to at least one vacuum pump. The exit of the vacuum pump, if necessary, is connected to a mechanism to condense and return pumped off vapors to the tank/tanks.
According to further embodiments, the container includes a hot air ventilator connected to the container interior. Also, it may include at least one ultrasound generator arranged in the container interior.
According to another embodiment, the drum, in an axial sectional view, can be xcfx89-shaped (similar to a ring-shaped cake tin opening towards the top) and include a perforated surface.
To reduce the amount of treatment fluid to be introduced, the container can directly and co-axially enclose the drum. Together with the drum, the container can be adjusted from an inclined axis position into a vertical axis position. An advantage of this design is that the required adjusting device can be arranged in uncomplicated surroundings outside the container and is thus easily accessible.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.